Recent advances in molecular genetics of glaucoma

Insights into the regulatory molecules involved in glaucoma pathogenesis

Glaucoma is an important cause of irreversible blindness, characterized by optic nerve anomalies. Increased intraocular pressure (IOP) and aging are major risk factors. Retinal ganglion cells and trabecular meshwork cells are certainly involved in the etiology of glaucoma. Glaucoma is usually a complex disease, and various genes and functions may contribute to its etiology. Among these may be genes that encode regulatory molecules. In this review, regulatory molecules including 18 transcription factors (TFs), 195 microRNAs (miRNAs), 106 long noncoding RNAs (lncRNAs), and two circular RNAs (circRNAs) that are reasonable candidates for having roles in glaucoma pathogenesis are described. The targets of the regulators are reported. Glaucoma-related features including apoptosis, stress responses, immune functions, ECM properties, IOP, and eye development are affected by the targeted genes. The targeted genes that are frequently targeted by multiple regulators most often affect apoptosis and the related features of cell death and cell survival. BCL2, CDKN1A, and TP53 are among the frequent targets of three types of glaucoma-relevant regulators, TFs, miRNAs, and lncRNAs. TP53 was itself identified as a glaucoma-relevant TF. Several of the glaucoma-relevant TFs are themselves among frequent targets of regulatory molecules, which is consistent with existence of a complex network involved in glaucoma pathogenesis.

Coding Variants in HOOK2 and GTPBP3 May Contribute to Risk of Primary Angle Closure Glaucoma

Primary angle closure glaucoma (PACG) is a major cause of blindness worldwide. This study proposed to screen candidate PACG-associated variants in Chinese Han people. Whole exome sequencing was applied to five confirmed PACG patients and two primary angle closure suspect individuals within a PACG-enriched Chinese Han family. A series of bioinformatics analyses were implemented to obtain high-risk single nucleotide variant (SNV) loci for PACG, which were subsequently used for linkage analysis for identifying linkage genome regions. In addition, MassARRAY SNV genotyping was applied to high-risk PACG loci as well as those within linkage regions in another independent cohort including 251 PACG and 251 normal samples to further screen high-confidence SNVs. A total of 27 loci in 19 genes remained after linkage analysis. The 19 genes were significantly enriched in biological processes tightly related to PACG, including retinol metabolism and salmonella infection. Two nonsynonymous SNV loci, rs897804 in exon15 of HOOK2 and rs3745193 in exon7 of GTPBP3, were recognized with higher variant frequency in PACG samples than that in control samples after association analysis of MassARRAY SNV genotyping data. This study sheds new light on the understanding of PACG incidence among Chinese Han people.

Genetic Basis of Primary Angle Closure Glaucoma: The Role of Collagens and Extracellular Matrix

This is an Editorial and does not have an abstract.

Integrative transcriptomic and proteomic analysis reveals CD9/ITGA4/PI3K-Akt axis mediates trabecular meshwork cell apoptosis in human glaucoma

Glaucoma has been the leading cause of irreversible blindness worldwide. High intraocular pressure (IOP) is a high‐risk factor of glaucoma, repression of which has been the important treatment of glaucoma in clinic. Trabecular meshwork is crucial for maintaining IOP in aqueous humour out‐flow system. It is urgent to reveal the molecular mechanism of trabecular meshwork in glaucoma. Previous studies found that some pathways were related to glaucoma, such as extracellular matrix (ECM)‐receptor interaction, phosphatidylinositol 3‐kinase (PI3K)‐protein kinase B (Akt) and apoptosis. To identify novel molecules in glaucoma, we performed high‐throughput transcriptome and proteome analysis to immortal human trabecular meshwork cells (iHTM) and glaucomatous human trabecular meshwork cells (GTM₃), respectively. Twenty‐six up‐regulated genes/proteins and 59 down‐regulated genes/proteins were identified as the high‐risk factors based on differential analysis, including some known factors of glaucoma. Furthermore, a glaucoma‐related protein‐protein interaction (PPI) network was constructed for investigating the function roles of risk factors. Some genes were identified as potential regulator in the pathogenesis of glaucoma based on the topology analysis and module analysis to the network. Importantly, we identified and demonstrated that CD9 played key roles in glaucoma by biological experiment. CD9 is down‐regulated in glaucoma, overexpression of CD9 can active integrin α4 (ITGA4), PI3K and Akt, which lead to the decreased apoptosis and attenuate glaucoma. All these results provide a novel molecular therapy of glaucoma.

COL18A1 is a candidate eye iridocorneal angle-closure gene in humans

Primary angle-closure glaucoma (PACG) is a common form of glaucoma in the Far East. Its defining feature is iridocorneal angle closure. In addition to PACG, indications of angle closure are included in the diagnostic criteria of related conditions primary angle-closure suspect (PACS) and primary angle closure (PAC). To the best of our knowledge, a causative gene for iridocorneal angle closure in humans has not been identified. This study aimed to identify the genetic cause of iridocorneal angle closure in a pedigree with at least 10 individuals diagnosed with PACS, PAC or PACG. Results of linkage analysis, segregation analysis of 44 novel variations, whole exome sequencing of 10 individuals, screenings of controls and bioinformatics predictions identified a mutation in COL18A1 that encodes collagen type XVIII as the most likely cause of angle closure in the pedigree. The role of COL18A1 in the etiology of Knobloch syndrome (KS) that is consistently accompanied by optic anomalies, available functional data on the encoded protein and the recognized role of collagens and the extracellular matrix in glaucoma pathogenesis supported the proposed role of the COL18A1 mutation in the pedigree. Subsequent identification of other COL18A1 mutations in PACS affected individuals of two unrelated families further supported that COL18A1 may affect angle closure. These PACS individuals were parents and grandparents of KS-affected children. In conclusion, a gene that affects angle closure in humans, a critical feature of PACG, has been identified. The findings also reinforce the importance of collagens in eye features and functions.

Estimating the age of the p.Cys433Arg variant in the MYOC gene in patients with primary open-angle glaucoma

The aim of this study was to estimate the age of the Cys433Arg (c.1297T>C, p.Cys433Arg) variant by comparing the genotypes of individuals affected and not affected by primary open angle glaucoma juvenile onset (JOAG). Our sample consisted of 35 JOAG-affected individuals from three families, 16 unrelated patients with the MYOC p.Cys433Arg variant and 16 unaffected individuals. Genomic DNA was amplified by PCR; nine short tandem repeats were genotyped through automated electrophoresis and three single nucleotide polymorphisms through Sanger sequencing. The determination of haplotypes was performed using Arlequin software and age estimation was performed using DMLE+ 2.3 and BDMC21 softwares. Four markers constituted the haplotypes associated with the p.Cys433Arg variant. The software DMLE+2.3 predicted an age of 43 generations for this variant with a 95% confidence interval ranging from 28 to 76 generations (560-1520 years) and BDMC21 predicted an age of 59 generations (1180 years) (95% CI: 40 to 100).

P.Gly61Glu and P.Arg368His Mutations in CYP1B1 that Cause Congenital Glaucoma may be Relatively Frequent in Certain Regions of Gilan Province, Iran

PURPOSE

To perform a population-based screening of four CYP1B1 mutations-p.Gly61Glu, p.Arg368His, p.Arg390His, and p.Arg469Trp-in the province of Gilan, Iran. Previous studies have shown that CYP1B1 is a cause of disease in approximately 70% of Iranian patients with primary congenital glaucoma (PCG), and that these four mutations constitute the majority of CYP1B1 mutated alleles. The carrier frequencies may even justify premarital screenings.

METHODS

DNA was extracted from the blood samples of 700 individuals recruited in a population-based epidemiology study in Gilan. Screenings were performed using polymerase chain reaction protocols based on restriction fragment length polymorphism or the amplification-refractory mutation system. For confirmation, the DNA of individuals with mutations was sequenced using the Sanger protocol.

RESULTS

Five individuals carried the p.Gly61Glu mutation, and seven carried the p.Arg368His mutation. The p.Arg390His and p.Arg469Trp mutations were not observed in any of the 700 individuals screened. The mutations were not geographically randomly distributed in Gilan; four of the p.Gly61Glu-harboring individuals were from Talesh, and six of the p.Arg368His-harboring individuals were from the eastern regions of Gilan.

CONCLUSION

The frequency of individuals who carry either p.Gly61Glu or p.Arg368His is relatively high in Gilan, and notably high in certain localities within Gilan. We suggest further screenings be performed to definitively assess the need for implementing measures to encourage screening for p.Gly61Glu and p.Arg368His before marriage in Talesh and the eastern regions of Gilan, respectively. Finally, our assessment showed that regional frequencies of CYP1B1 mutations do not necessarily mirror national frequencies.

LTBP2 knockdown and oxidative stress affect glaucoma features including TGFβ pathways, ECM genes expression and apoptosis in trabecular meshwork cells

Glaucoma is the leading cause of irreversible blindness worldwide. Although the etiology of glaucoma is incompletely understood, it is known that the extracellular matrix (ECM) of the trabecular meshwork, oxidative stress, TGFβ signaling pathways, and apoptosis are important components of glaucoma pathogenesis. These components appear to be interrelated, but knowledge on their interactions remains incomplete. Relevant to this gap in knowledge, LTBP2, glaucoma causing gene, may also be related to the mentioned components of glaucoma pathogenesis because of its putative roles in TGFβ signaling and ECM functions. This background prompted us to further query interactions among some molecules and pathways thought to be important in glaucoma etiology, with emphasis on oxidative stress and LTBP2. To this end, effects of LTBP2 siRNA knockdown, oxidative stress induction, TGFβ2 and gremlin exposures on canonical TGFβ and BMP signaling pathways, expression of ECM related genes, and apoptosis were assayed in primary human trabecular meshwork cell cultures. We found that oxidative stress induction and LTBP2 knockdown both affected all the processes queried, and that their affects paralleled one another. We suggest that effects of both oxidative stress and LTBP2 knockdown on the ECM and apoptosis may be mediated by TGFβ and BMP signaling pathway activation.

Candidate Gene Analysis Identifies Mutations in CYP1B1 and LTBP2 in Indian Families with Primary Congenital Glaucoma

BACKGROUND

Primary congenital glaucoma (PCG) is a severe ocular disorder that presents early in life. Cytochrome P4501B1 (CYP1B1) and latent transforming growth factor-beta-binding protein 2 (LTBP2) are the most commonly mutated genes in PCG.

AIM

To investigate the causative genetic mutations in eight Indian families with PCG.

MATERIALS AND METHODS

Whole-exome sequencing was applied to analyze the genomic DNA samples from PCG probands. Sanger sequencing was utilized to confirm the identified mutations.

RESULTS

We identified four homozygous missense mutations (c.1405C>T, p.R469W; c.1397G>T, p.G466V; c.1198C>T, p.P400S; and c.1103G>A, p.R368H) in CYP1B1 and one nonsense mutation (c.2421G>A, p.W807X) in LTBP2 in eight Indian families. Among the five mutations identified, G466V in CYP1B1 and W807X in LTBP2 represent novel mutations.

CONCLUSIONS

Our study expands the mutational spectrum of PCG in the Indian population.

Genetic and Biochemical Biomarkers in Canine Glaucoma

In many health-related fields, there is great interest in the identification of biomarkers that distinguish diseased from healthy individuals. In addition to identifying the diseased state, biomarkers have potential use in predicting disease risk, monitoring disease progression, evaluating treatment efficacy, and informing pathogenesis. This review details the genetic and biochemical markers associated with canine primary glaucoma. While there are numerous molecular markers (biochemical and genetic) associated with glaucoma in dogs, there is no ideal biomarker that allows early diagnosis and/or identification of disease progression. Genetic mutations associated with canine glaucoma include those affecting ADAMTS10, ADAMTS17, Myocilin, Nebulin, COL1A2, RAB22A, and SRBD1. With the exception of Myocilin, there is very limited crossover in genetic biomarkers identified between human and canine glaucomas. Mutations associated with canine glaucoma vary between and within canine breeds, and gene discoveries therefore have limited overall effects as a screening tool in the general canine population. Biochemical markers of glaucoma include indicators of inflammation, oxidative stress, serum autoantibodies, matrix metalloproteinases, tumor necrosis factor–α, and transforming growth factor–β. These markers include those that indicate an adaptive or protective response, as well as those that reflect the damage arising from oxidative stress.

A spectrum of CYP1B1 mutations associated with primary congenital glaucoma in families of Pakistani descent

Glaucoma is the second leading cause of blindness, affecting ~65 million people worldwide. We identified and ascertained a large cohort of inbred families with multiple individuals manifesting cardinal symptoms of primary congenital glaucoma (PCG) to investigate the etiology of the disease at a molecular level. Ophthalmic examinations, including slit-lamp microscopy and applanation tonometry, were performed to characterize the causal phenotype and confirm that affected individuals fulfilled the diagnostic criteria for PCG. Subsequently, exclusion analysis was completed with fluorescently labeled short tandem repeat markers, followed by Sanger sequencing to identify pathogenic variants. Exclusion analysis suggested linkage to the CYP1B1 locus, with positive two-point logarithm of odds scores in 23 families, while Sanger sequencing identified a total of 11 variants, including two novel mutations, in 23 families. All mutations segregated with the disease phenotype in their respective families. These included the following seven missense mutations: p.Y81N, p.E229K, p.R368H, p.R390H, p.W434R, p.R444Q and p.R469W, as well as one nonsense mutation, p.Q37*, and three frameshift mutations, p.W246Lfs81*, p.T404Sfs30* and p.P442Qfs15*. In conclusion, we identified a total of 11 mutations, reconfirming the genetic heterogeneity of CYP1B1 in the pathogenesis of PCG. To the best of our knowledge, this is the largest study investigating the contribution of CYP1B1 to the pathogenesis of PCG in the Pakistani population.

Glaucoma in iran and contributions of studies in iran to the understanding of the etiology of glaucoma

Epidemiologic and genetic/molecular research on glaucoma in Iran started within the past decade. A population-based study on the epidemiology of glaucoma in Yazd, a city in central Iran, revealed that 4.4% of studied individuals were affected with glaucoma: 1.6% with high tension primary open angle glaucoma (POAG), 1.6% with normal tension POAG, and 0.4% each with primary angle closure glaucoma (PACG) and pseudoexfoliation glaucoma (PEXG), and other types of secondary glaucoma. Two notable observations were the relatively high frequency of normal tension glaucoma cases (1.6%) and the large fraction of glaucoma affected individuals (nearly 90%) who were unaware of their condition. The first and most subsequent genetic studies on glaucoma in Iran were focused on primary congenital glaucoma (PCG) showing that cytochrome P450 1B1 (CYP1B1) is the cause of PCG in the majority of Iranian patients, many different CYP1B1 mutations are present among Iranian patients but only four mutations constitute the vast majority, and the origins of most mutations in the Iranians are identical by descent (IBD) with the same mutations in other populations. Furthermore, most of the PCG patients are from the northern and northwestern provinces of Iran. A statistically significant male predominance of PCG was observed only among patients without CYP1B1 mutations. Clinical investigations on family members of PCG patients revealed that CYP1B1 mutations exhibit variable expressivity, but almost complete penetrance. A great number of individuals harboring CYP1B1 mutations become affected with juvenile onset POAG. Screening of JOAG patients showed that an approximately equal fraction of the patients harbor CYP1B1 and (myocilin) MYOC mutations; MYOC is a well-known adult onset glaucoma causing gene. Presence of CYP1B1 mutations in JOAG patients suggests that in some cases, the two conditions may share a common etiology. Further genetic analysis of Iranian PCG patients led to identification of Latent-transforming growth factor beta-binding protein 2 (LTBP2) as a causative gene for both PCG and several diseases which are often accompanied by glaucomatous presentations, such as Weill-Marchesani syndrome 3 (WMS3). The findings on LTBP2 have contributed to recognize the importance of the extracellular matrix in pathways leading to glaucoma.

Genome-wide association study identifies a novel canine glaucoma locus

Glaucoma is an optic neuropathy and one of the leading causes of blindness. Its hereditary forms are classified into primary closed-angle (PCAG), primary open-angle (POAG) and primary congenital glaucoma (PCG). Although many loci have been mapped in human, only a few genes have been identified that are associated with the development of glaucoma and the genetic basis of the disease remains poorly understood. Glaucoma has also been described in many dog breeds, including Dandie Dinmont Terriers (DDT) in which it is a late-onset (>7 years) disease. We designed clinical and genetic studies to better define the clinical features of glaucoma in the DDT and to identify the genetic cause. Clinical diagnosis was based on ophthalmic examinations of the affected dogs and 18 additionally investigated unaffected DDTs. We collected DNA from over 400 DTTs and a genome wide association study was performed in a cohort of 23 affected and 23 controls, followed by a fine mapping, a replication study and candidate gene sequencing. The clinical study suggested that ocular abnormalities including abnormal iridocorneal angles and pectinate ligament dysplasia are common (50% and 72%, respectively) in the breed and the disease resembles human PCAG. The genetic study identified a novel 9.5 Mb locus on canine chromosome 8 including the 1.6 Mb best associated region (p = 1.63 × 10(-10), OR = 32 for homozygosity). Mutation screening in five candidate genes did not reveal any causative variants. This study indicates that although ocular abnormalities are common in DDTs, the genetic risk for glaucoma is conferred by a novel locus on CFA8. The canine locus shares synteny to a region in human chromosome 14q, which harbors several loci associated with POAG and PCG. Our study reveals a new locus for canine glaucoma and ongoing molecular studies will likely help to understand the genetic etiology of the disease.

New mutation in the myocilin gene segregates with juvenile-onset open-angle glaucoma in a Brazilian family

Mutations in the myocilin gene (MYOC) account for most cases of autosomal dominant juvenile-onset open-angle glaucoma (JOAG), an earlier and more severe form of POAG. We accessed seven members of a Brazilian JOAG family by clinical and molecular investigation. Four out of seven family members were diagnosed with JOAG. All of these patients presented high intraocular pressure and two of them were bilaterally blind. The disease onset varied from 20 to 30years old. There was a nine-year-old family member who had not yet manifested the disease, although he was also a carrier of the mutation. Ophthalmologic examination included: evaluation of the visual field and optic disc, intraocular pressure measurement, and gonioscopy. The three exons and intron/exon junctions of the MYOC gene were screened for mutations through direct sequencing of PCR-amplified DNA fragments. Mutation screening revealed an in-frame mutation in the third exon of the MYOC gene: an insertion of six nucleotides between the cDNA positions 1187 and 1188 (c.1187_1188insCCCAGA, p.D395_E396insDP). This mutation presented an autosomal dominant pattern of inheritance, segregating with the disease in four family members for three generations, and it was absent in 60 normal controls. We also performed a computational structure modeling of olfactomedin-like domain of myocilin protein and conducted in silico analysis to predict the structural changes in the myocilin protein due to the presence of the mutation. These findings may be important for future diagnosis of other presymptomatic family members, as well as for the increase of the panel of MYOC mutations and their effects on phenotype.

Molecular analysis of Italian patients with congenital glaucoma

Purpose: Congenital glaucoma (CG) results from poorly understood developmental abnormalities of the aqueous drainage structures and is clinically characterized by high intraocular pressure (IOP), epiphora, corneal oedema, photophobia, blepharospasm and ocular enlargement. To date, more than 50 pathogenic mutations in the CYP1B1 gene, a member of the cytochrome P450 gene family, have been reported in CG patients. The aim of this paper was to determine the genetic defects underlying CG in Italian patients. Methods: Molecular analysis of CYP1B1 was performed on the DNA of 120 patients and the transcript region of the MYOC/TIGR gene was also studied in all the patients bearing only one mutation in CYP1B1 gene. Previously described CYP1B1 polymorphisms (R48G, A119S, L432V, D449D and N453S) were also analyzed in our patients. Results: Seventeen different variations of CYP1B1 were found in 30 of the 120 (25.0%) CG patients. Twelve of these changes had been identified in previous reports as disease-causing mutations, while L26R, P52L, A106D, A237E and F440L are described here for the first time. F440L has always been found in cis with P52L, both in patients and healthy carriers, suggesting its role as a rare polymorphism linked to the P52L, while the other new variations we found could possibly play a pathogenetic role. G61E and 1775-1801dup27 are the most frequent mutations in our patients. Two amino acid variations (A447V and R76K) were identified in MYOC/TIGR analysis. Conclusions: Our results confirm the major role of the CYP1B1 gene in congenital glaucoma and also suggest an autosomal recessive role of MYOC/TIGR in a digenic inheritance model.

Neuroprotection in glaucoma - Is there a future role?

In glaucoma, the major cause of global irreversible blindness, there is an urgent need for treatment modalities that directly target the RGCs. The discovery of an alternative therapeutic approach, independent of IOP reduction, is highly sought after, due to the indirect nature and limited effectiveness of IOP lowering therapy in preventing RGC loss. Several mechanisms have been implicated in initiating the apoptotic cascade in glaucomatous retinopathy and numerous drugs have been shown to be neuroprotective in animal models of glaucoma. These mechanisms and their potential treatment include excitotoxicity, protein misfolding, mitochondrial dysfunction, oxidative stress, inflammation and neurotrophin deprivation. All of these mechanisms ultimately lead to programmed cell death with loss of RGCs. In this article we summarize the mechanisms involved in glaucomatous disease, highlight the rationale for neuroprotection in glaucoma management and review current potential neuroprotective strategies targeting RGCs from the laboratory to the clinic.

Molecular complexity of primary open angle glaucoma: current concepts

Glaucoma is a group of heterogeneous optic neuropathies with complex genetic basis. Among the three principle subtypes of glaucoma, primary open angle glaucoma (POAG) occurs most frequently. Till date, 25 loci have been found to be linked to POAG. However, only three underlying genes (Myocilin, Optineurin and WDR36) have been identified. In addition, at least 30 other genes have been reported to be associated with POAG. Despite strong genetic influence in POAG pathogenesis, only a small part of the disease can be explained in terms of genetic aberration. Current concepts of glaucoma pathogenesis suggest it to be a neurodegenerative disorder which is triggered by different factors including mechanical stress due to intra-ocular pressure, reduced blood flow to retina, reperfusion injury, oxidative stress, glutamate excitotoxicity, and aberrant immune response. Here we present a mechanistic overview of potential pathways and crosstalk between them operating in POAG pathogenesis.

Loss of function mutations in the gene encoding latent transforming growth factor beta binding protein 2, LTBP2, cause primary congenital glaucoma

Glaucoma is a heterogeneous group of optic neuropathies that manifests by optic nerve head cupping or degeneration of the optic nerve, resulting in a specific pattern of visual field loss. Glaucoma leads to blindness if left untreated, and is considered the second leading cause of blindness worldwide. The subgroup primary congenital glaucoma (PCG) is characterized by an anatomical defect in the trabecular meshwork, and age at onset in the neonatal or infantile period. It is the most severe form of glaucoma. CYP1B1 was the first gene genetically linked to PCG, and CYP1B1 mutations are the cause of disease in 20-100% of patients in different populations. Here, we report that LTBP2 encoding latent transforming growth factor beta binding protein 2 is a PCG causing gene, confirming results recently reported. A disease-associated locus on chromosome 14 was identified by performing whole genome autozygosity mapping in Iranian PCG families using high density single nucleotide polymorphism chips, and two disease-segregating loss of function mutations in LTBP2, p.Ser472fsX3 and p.Tyr1793fsX55, were observed in two families while sequencing candidate genes in the locus. The p.Tyr1793fsX55 mutation affects an amino acid close to the C-terminal of the encoded protein. Subsequently, LTBP2 expression was shown in human eyes, including the trabecular meshwork and ciliary processes that are thought to be relevant to the etiology of PCG.

Structural features and functional domains of amassin-1, a cell-binding olfactomedin protein

Amassin-1 mediates a rapid cell adhesion that tightly adheres sea urchin coelomocytes (body cavity immunocytes) together. Three major structural regions exist in amassin-1: a short beta region, 3 coiled coils, and an olfactomedin domain. Amassin-1 contains 8 disulfide-bonded cysteines that, upon reduction, render it inactive. Truncated forms of recombinant amassin-1 were expressed and purified from Pichia pastoris and their disulfide bonding and biological activities investigated. Expressed alone, the olfactomedin domain contained 2 intramolecular disulfide bonds, existed in a monomeric state, and inhibited amassin-1-mediated clotting of coelomocytes by a calcium-dependent cell-binding activity. The N-terminal beta region, containing 3 cysteines, was not required for clotting activity. The coiled coils may dimerize amassin-1 in a parallel orientation through a homodimerizing disulfide bond. Neither amassin-1 fragments that were disulfide-linked as dimers or that were engineered to exist as dimers induced coelomocytes clotting. Clotting required higher multimeric states of amassin-1, possibly tetramers, which occurred through the N-terminal beta region and (or) the first segment of coiled coils.

Cloning of canine myocilin cDNA and molecular analysis of the myocilin gene in Shiba Inu dogs

OBJECTIVE

To identify canine myocilin cDNA and compare its sequence in glaucomatous and nonglaucomatous Shiba Inu dogs with closed and open iridocorneal angles (ICAs).

PROCEDURES

Total RNA was extracted from the ciliary body of the eyes of a healthy Beagle, and the canine myocilin gene was cloned and sequenced. Of the Shiba Inu dogs tested, five were glaucomatous with closed ICA, three were nonglaucomatous with open ICA, and two were nonglaucomatous with closed ICA. The genomic DNA of these dogs was extracted from peripheral blood leukocytes. The exons of the canine myocilin gene were amplified using the polymerase chain reaction (PCR), and sequenced. The frequency of mutation in canine myocilin DNA was verified in these dogs by using the myocilin cDNA of a Beagle.

RESULTS

The canine myocilin cDNA was 1452 bp long and contained the entire open reading frame encoding 483 amino acids. A leucine zipper-like motif and olfactomedin-like domain were conserved in the amino acid residues. The presence of sequence variants in the genomic DNA of Shiba Inu dogs was independent of the occurrence of glaucoma and ICA grading.

CONCLUSIONS

Myocilin RNA was detected in the ciliary body and trabecular meshwork (TM) of a Beagle. The myocilin sequence of Shiba Inu dogs suggests that myocilin mutations are unlikely to play a significant role in the pathogenesis of primary closed-angle glaucoma in this breed. However, several mutations in the myocilin gene in exon 1 of Shiba Inu dogs may predispose them to an obstruction in the anterior aqueous outflow.

Abnormal iris processes may be a marker of glaucoma gene carrier status in some cases of primary infantile glaucoma

PURPOSE

To report the presence of dense and abnormal iris processes in the unaffected parents and sibling of a non consanguineous family where 3 children out of 4 suffer from primary infantile glaucoma (PIG).

METHODS

A descriptive case report. All family members were clinically characterized. Candidate gene screening and chromosome analysis were also performed.

RESULTS

The 3 children with PIG displayed a spectrum of anterior chamber angle anomalies with the absence of posterior embryotoxon and iridotrabeculodysgenesis abnormalities. Unaffected family members had dense and abnormal iris processes but no features of glaucoma. Candidate gene screening and chromosome analysis were normal.

CONCLUSION

Iris processes indicate angle maldevelopment and may signify carrier status of an autosomal recessive glaucoma gene. Identification of iris processes in relatives of PIG children is a useful clinical sign that may be of benefit for genetic counseling and risk stratification purposes.

CYP1B1 mutation profile of Iranian primary congenital glaucoma patients and associated haplotypes

The mutation spectrum of CYP1B1 among 104 primary congenital glaucoma patients of the genetically heterogeneous Iranian population was investigated by sequencing. We also determined intragenic single nucleotide polymorphism (SNP) haplotypes associated with the mutations and compared these with haplotypes of other populations. Finally, the frequency distribution of the haplotypes was compared among primary congenital glaucoma patients with and without CYP1B1 mutations and normal controls. Genotype classification of six high-frequency SNPs was performed using the PHASE 2.0 software. CYP1B1 mutations in the Iranian patients were very heterogeneous. Nineteen nonconservative mutations associated with disease, and 10 variations not associated with disease were identified. Ten mutations and three variations not associated with disease were novel. The 13 novel variations make a notable contribution to the approximately 70 known variations in the gene. CYP1B1 mutations were identified in 70% of the patients. The four most common mutations were G61E, R368H, R390H, and R469W, which together constituted 76.2% of the CYP1B1 mutated alleles found. Six unique core SNP haplotypes were identified, four of which were common to the patients with and without CYP1B1 mutations and controls studied. Three SNP blocks determined the haplotypes. Comparison of haplotypes with those of other populations suggests a common origin for many of the mutations.

Diversity of olfactomedin proteins in the sea urchin

Olfactomedin (OLF) domain proteins maintain extracellular protein-protein interactions in diverse phyla. Only one OLF family member, amassin-1, has been described from the sea urchin Strongylocentrotus purpuratus, a basal invertebrate deuterostome. Amassin-1 mediates intercellular adhesion of coelomocytes (immunocytes). Here we describe the protein structural features of four additional OLF proteins, the total for the genome being five. Phylogenetically, four of these proteins (the amassins) form a subgroup among previously identified OLF proteins. The fifth OLF protein is within the colmedin subfamily and contains a type II transmembrane domain, collagen repeats, and an OLF domain. Sea urchin OLF proteins represent an intermediate diversification between protostomes and vertebrates. Transcripts of all five OLF family members are in coelomocytes and adult radial nerve tissue. Transcripts for some OLF proteins increase during late larval stages. Transcript levels for amassin-1 increase 1,000,000-fold, coinciding with formation of the adult urchin rudiment within the larval body.

Expression of m-Golsyn/Syntabulin gene during mouse brain development

We recently isolated the cDNA for the mouse Golsyn/Syntabulin (m-Golsyn/Syntabulin) gene and mapped it to mouse chromosome 15B3.2 syntenic with human chromosome 8q23, on which a locus responsible for primary open-angle glaucoma had been located. In the present study, we examined the expression of m-Golsyn/Syntabulin protein in various regions of mouse brain and its developmental changes by use of anti-GOLSYN antibody. m-Golsyn/Syntabulin protein was detected in various brain regions at embryonic day 14 and throughout the postnatal stages. Furthermore, as the histogenesis and maturation of brain proceeded, strong expression of the protein became detectable in cells of the choroid plexus, piriform cortex, pyramidal cell layer, and Purkinje cell layer. In situ hybridization analysis of the mouse brain revealed that localization of the m-Golsyn/Syntabulin transcript was very similar to that of m-Golsyn/Syntabulin protein, confirming the high-level expression of the m-Golsyn/Syntabulin gene in the specific brain regions. High-level expression of m-Golsyn/Syntabulin protein was also observed in the ocular tissues including the ciliary body, which is known as a site for the production of aqueous humor. These results may indicate a significant role for this protein in neuronal cells and other types of cells such as those of the choroid plexus and ciliary body.

Molecular cloning of the m-Golsyn gene and its expression in the mouse brain

The mouse ortholog of the human GOLSYN gene, termed the m-Golsyn gene, was isolated and mapped to the region on mouse chromosome 15B3.2 syntenic with human chromosome 8q23. Three mRNA species (type la, 1b, and type 2) were produced by use of alternative transcription initiation points and alternative splicing events. The type 1 mRNAs were expressed only in the brain, whereas the type 2 was detected in various tissues. m-Golsyn protein was expressed in various tissues including the brain. Immunohistochemical study of m-Golsyn protein showed its prominent expression in the neuronal cells in various regions of the brain and strong expression in the choroid plexus ependymal cells lining the ventricles. m-Golsyn protein was found to be homologous to syntaphilin, a regulator of synaptic vesicle exocytosis. These results indicate that the m-Golsyn protein may play an important role in intracellular protein transport in neuronal cells of the brain.

Expression, purification, crystallization and preliminary X-ray analysis of the olfactomedin domain from the sea urchin cell-adhesion protein amassin

A family of animal proteins is emerging which contain a conserved protein motif known as an olfactomedin (OLF) domain. Novel extracellular protein-protein interactions occur through this domain. The OLF-family member amassin, from the sea urchin Strongylocentrotus purpuratus, has previously been identified to mediate a rapid cell-adhesion event resulting in a large aggregation of coelomocytes, the circulating immune cells. In this work, heterologous expression and purification of the OLF domain from amassin was carried out and initial crystallization trials were performed. A native data set has been collected, extending to 2.7 A under preliminary cryoconditions, using an in-house generator. This work leads the way to the determination of the first structure of an OLF domain.